Headlight Short Circuit

Tech Question


Brad Toovey, Sundre, AB, Canada, 1963 Plymouth Valiant 170

Hello Mr Ehrenberg,
Here we go again, I’ve had to plead help in the past, and you’ve comethrough both times. That being said, I’m using the ‘bribe’ option, asopposed to kissing ass.

About a year ago, I did the headlamp relay conversion as per the Sternlighting website on my ’63 Valiant. It worked beautifully, giving the ol’girl better lighting than either of the late-model plastic wrecks thatcomprise the rest of the household fleet. However, 6 odd weeks ago, thedriver’s side lamp burned out. I replaced it, 3 weeks after that,both sidesburned out(although the right took a rather large rock). Now, both lampshave crapped out again,this time on both the high and low beam circuits. Thehighs gave up at precisely the same time, cause I watched ’em, with no smallamount of panic. I’ve given the relay connections the once-over, no ‘greendisease’or anything obvious. I stabbed in a non-halogen lamp I had lyingaround,it works, it’s getting 12.0 volts on both sides,and no hugeresistance in the wiring. All replacement lamps have been GE halogens. Anyideas?

Thanks in advance.


Brad, best guess: Intermittent short in the alternator’s rotating fieldwinding, causing the regulator to lose control and the battery voltage tomomentatily go very high. Poof!

Second place guess: Sticky contacts in electromechanical voltage regulator.